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bpf: allow programs to write to certain skb fields

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allow programs read/write skb->mark, tc_index fields and
((struct qdisc_skb_cb *)cb)->data.

mark and tc_index are generically useful in TC.
cb[0]-cb[4] are primarily used to pass arguments from one
program to another called via bpf_tail_call() which can
be seen in sockex3_kern.c example.

All fields of 'struct __sk_buff' are readable to socket and tc_cls_act progs.
mark, tc_index are writeable from tc_cls_act only.
cb[0]-cb[4] are writeable by both sockets and tc_cls_act.

Add verifier tests and improve sample code.

Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Alexei Starovoitov 2015-06-04 10:11:54 -07:00 committed by David S. Miller
parent 3431205e03
commit d691f9e8d4
6 changed files with 207 additions and 48 deletions
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3
include/linux/bpf.h
View File

@ -105,7 +105,8 @@ struct bpf_verifier_ops {
*/
bool (*is_valid_access)(int off, int size, enum bpf_access_type type);
u32 (*convert_ctx_access)(int dst_reg, int src_reg, int ctx_off,
u32 (*convert_ctx_access)(enum bpf_access_type type, int dst_reg,
int src_reg, int ctx_off,
struct bpf_insn *insn);
};

2
include/uapi/linux/bpf.h
View File

@ -248,6 +248,8 @@ struct __sk_buff {
__u32 priority;
__u32 ingress_ifindex;
__u32 ifindex;
__u32 tc_index;
__u32 cb[5];
};
#endif /* _UAPI__LINUX_BPF_H__ */

37
kernel/bpf/verifier.c
View File

@ -1692,6 +1692,8 @@ static int do_check(struct verifier_env *env)
}
} else if (class == BPF_STX) {
enum bpf_reg_type dst_reg_type;
if (BPF_MODE(insn->code) == BPF_XADD) {
err = check_xadd(env, insn);
if (err)
@ -1700,11 +1702,6 @@ static int do_check(struct verifier_env *env)
continue;
}
if (BPF_MODE(insn->code) != BPF_MEM ||
insn->imm != 0) {
verbose("BPF_STX uses reserved fields\n");
return -EINVAL;
}
/* check src1 operand */
err = check_reg_arg(regs, insn->src_reg, SRC_OP);
if (err)
@ -1714,6 +1711,8 @@ static int do_check(struct verifier_env *env)
if (err)
return err;
dst_reg_type = regs[insn->dst_reg].type;
/* check that memory (dst_reg + off) is writeable */
err = check_mem_access(env, insn->dst_reg, insn->off,
BPF_SIZE(insn->code), BPF_WRITE,
@ -1721,6 +1720,15 @@ static int do_check(struct verifier_env *env)
if (err)
return err;
if (insn->imm == 0) {
insn->imm = dst_reg_type;
} else if (dst_reg_type != insn->imm &&
(dst_reg_type == PTR_TO_CTX ||
insn->imm == PTR_TO_CTX)) {
verbose("same insn cannot be used with different pointers\n");
return -EINVAL;
}
} else if (class == BPF_ST) {
if (BPF_MODE(insn->code) != BPF_MEM ||
insn->src_reg != BPF_REG_0) {
@ -1839,12 +1847,18 @@ static int replace_map_fd_with_map_ptr(struct verifier_env *env)
for (i = 0; i < insn_cnt; i++, insn++) {
if (BPF_CLASS(insn->code) == BPF_LDX &&
(BPF_MODE(insn->code) != BPF_MEM ||
insn->imm != 0)) {
(BPF_MODE(insn->code) != BPF_MEM || insn->imm != 0)) {
verbose("BPF_LDX uses reserved fields\n");
return -EINVAL;
}
if (BPF_CLASS(insn->code) == BPF_STX &&
((BPF_MODE(insn->code) != BPF_MEM &&
BPF_MODE(insn->code) != BPF_XADD) || insn->imm != 0)) {
verbose("BPF_STX uses reserved fields\n");
return -EINVAL;
}
if (insn[0].code == (BPF_LD | BPF_IMM | BPF_DW)) {
struct bpf_map *map;
struct fd f;
@ -1967,12 +1981,17 @@ static int convert_ctx_accesses(struct verifier_env *env)
struct bpf_prog *new_prog;
u32 cnt;
int i;
enum bpf_access_type type;
if (!env->prog->aux->ops->convert_ctx_access)
return 0;
for (i = 0; i < insn_cnt; i++, insn++) {
if (insn->code != (BPF_LDX | BPF_MEM | BPF_W))
if (insn->code == (BPF_LDX | BPF_MEM | BPF_W))
type = BPF_READ;
else if (insn->code == (BPF_STX | BPF_MEM | BPF_W))
type = BPF_WRITE;
else
continue;
if (insn->imm != PTR_TO_CTX) {
@ -1982,7 +2001,7 @@ static int convert_ctx_accesses(struct verifier_env *env)
}
cnt = env->prog->aux->ops->
convert_ctx_access(insn->dst_reg, insn->src_reg,
convert_ctx_access(type, insn->dst_reg, insn->src_reg,
insn->off, insn_buf);
if (cnt == 0 || cnt >= ARRAY_SIZE(insn_buf)) {
verbose("bpf verifier is misconfigured\n");

94
net/core/filter.c
View File

@ -46,6 +46,7 @@
#include <linux/seccomp.h>
#include <linux/if_vlan.h>
#include <linux/bpf.h>
#include <net/sch_generic.h>
/**
* sk_filter - run a packet through a socket filter
@ -1463,13 +1464,8 @@ tc_cls_act_func_proto(enum bpf_func_id func_id)
}
}
static bool sk_filter_is_valid_access(int off, int size,
enum bpf_access_type type)
static bool __is_valid_access(int off, int size, enum bpf_access_type type)
{
/* only read is allowed */
if (type != BPF_READ)
return false;
/* check bounds */
if (off < 0 || off >= sizeof(struct __sk_buff))
return false;
@ -1485,8 +1481,42 @@ static bool sk_filter_is_valid_access(int off, int size,
return true;
}
static u32 sk_filter_convert_ctx_access(int dst_reg, int src_reg, int ctx_off,
struct bpf_insn *insn_buf)
static bool sk_filter_is_valid_access(int off, int size,
enum bpf_access_type type)
{
if (type == BPF_WRITE) {
switch (off) {
case offsetof(struct __sk_buff, cb[0]) ...
offsetof(struct __sk_buff, cb[4]):
break;
default:
return false;
}
}
return __is_valid_access(off, size, type);
}
static bool tc_cls_act_is_valid_access(int off, int size,
enum bpf_access_type type)
{
if (type == BPF_WRITE) {
switch (off) {
case offsetof(struct __sk_buff, mark):
case offsetof(struct __sk_buff, tc_index):
case offsetof(struct __sk_buff, cb[0]) ...
offsetof(struct __sk_buff, cb[4]):
break;
default:
return false;
}
}
return __is_valid_access(off, size, type);
}
static u32 bpf_net_convert_ctx_access(enum bpf_access_type type, int dst_reg,
int src_reg, int ctx_off,
struct bpf_insn *insn_buf)
{
struct bpf_insn *insn = insn_buf;
@ -1538,7 +1568,15 @@ static u32 sk_filter_convert_ctx_access(int dst_reg, int src_reg, int ctx_off,
break;
case offsetof(struct __sk_buff, mark):
return convert_skb_access(SKF_AD_MARK, dst_reg, src_reg, insn);
BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, mark) != 4);
if (type == BPF_WRITE)
*insn++ = BPF_STX_MEM(BPF_W, dst_reg, src_reg,
offsetof(struct sk_buff, mark));
else
*insn++ = BPF_LDX_MEM(BPF_W, dst_reg, src_reg,
offsetof(struct sk_buff, mark));
break;
case offsetof(struct __sk_buff, pkt_type):
return convert_skb_access(SKF_AD_PKTTYPE, dst_reg, src_reg, insn);
@ -1553,6 +1591,38 @@ static u32 sk_filter_convert_ctx_access(int dst_reg, int src_reg, int ctx_off,
case offsetof(struct __sk_buff, vlan_tci):
return convert_skb_access(SKF_AD_VLAN_TAG,
dst_reg, src_reg, insn);
case offsetof(struct __sk_buff, cb[0]) ...
offsetof(struct __sk_buff, cb[4]):
BUILD_BUG_ON(FIELD_SIZEOF(struct qdisc_skb_cb, data) < 20);
ctx_off -= offsetof(struct __sk_buff, cb[0]);
ctx_off += offsetof(struct sk_buff, cb);
ctx_off += offsetof(struct qdisc_skb_cb, data);
if (type == BPF_WRITE)
*insn++ = BPF_STX_MEM(BPF_W, dst_reg, src_reg, ctx_off);
else
*insn++ = BPF_LDX_MEM(BPF_W, dst_reg, src_reg, ctx_off);
break;
case offsetof(struct __sk_buff, tc_index):
#ifdef CONFIG_NET_SCHED
BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, tc_index) != 2);
if (type == BPF_WRITE)
*insn++ = BPF_STX_MEM(BPF_H, dst_reg, src_reg,
offsetof(struct sk_buff, tc_index));
else
*insn++ = BPF_LDX_MEM(BPF_H, dst_reg, src_reg,
offsetof(struct sk_buff, tc_index));
break;
#else
if (type == BPF_WRITE)
*insn++ = BPF_MOV64_REG(dst_reg, dst_reg);
else
*insn++ = BPF_MOV64_IMM(dst_reg, 0);
break;
#endif
}
return insn - insn_buf;
@ -1561,13 +1631,13 @@ static u32 sk_filter_convert_ctx_access(int dst_reg, int src_reg, int ctx_off,
static const struct bpf_verifier_ops sk_filter_ops = {
.get_func_proto = sk_filter_func_proto,
.is_valid_access = sk_filter_is_valid_access,
.convert_ctx_access = sk_filter_convert_ctx_access,
.convert_ctx_access = bpf_net_convert_ctx_access,
};
static const struct bpf_verifier_ops tc_cls_act_ops = {
.get_func_proto = tc_cls_act_func_proto,
.is_valid_access = sk_filter_is_valid_access,
.convert_ctx_access = sk_filter_convert_ctx_access,
.is_valid_access = tc_cls_act_is_valid_access,
.convert_ctx_access = bpf_net_convert_ctx_access,
};
static struct bpf_prog_type_list sk_filter_type __read_mostly = {

35
samples/bpf/sockex3_kern.c
View File

@ -89,7 +89,6 @@ static inline __u32 ipv6_addr_hash(struct __sk_buff *ctx, __u64 off)
struct globals {
struct flow_keys flow;
__u32 nhoff;
};
struct bpf_map_def SEC("maps") percpu_map = {
@ -139,7 +138,7 @@ static void update_stats(struct __sk_buff *skb, struct globals *g)
static __always_inline void parse_ip_proto(struct __sk_buff *skb,
struct globals *g, __u32 ip_proto)
{
__u32 nhoff = g->nhoff;
__u32 nhoff = skb->cb[0];
int poff;
switch (ip_proto) {
@ -165,7 +164,7 @@ static __always_inline void parse_ip_proto(struct __sk_buff *skb,
if (gre_flags & GRE_SEQ)
nhoff += 4;
g->nhoff = nhoff;
skb->cb[0] = nhoff;
parse_eth_proto(skb, gre_proto);
break;
}
@ -195,7 +194,7 @@ PROG(PARSE_IP)(struct __sk_buff *skb)
if (!g)
return 0;
nhoff = g->nhoff;
nhoff = skb->cb[0];
if (unlikely(ip_is_fragment(skb, nhoff)))
return 0;
@ -210,7 +209,7 @@ PROG(PARSE_IP)(struct __sk_buff *skb)
verlen = load_byte(skb, nhoff + 0/*offsetof(struct iphdr, ihl)*/);
nhoff += (verlen & 0xF) << 2;
g->nhoff = nhoff;
skb->cb[0] = nhoff;
parse_ip_proto(skb, g, ip_proto);
return 0;
}
@ -223,7 +222,7 @@ PROG(PARSE_IPV6)(struct __sk_buff *skb)
if (!g)
return 0;
nhoff = g->nhoff;
nhoff = skb->cb[0];
ip_proto = load_byte(skb,
nhoff + offsetof(struct ipv6hdr, nexthdr));
@ -233,25 +232,21 @@ PROG(PARSE_IPV6)(struct __sk_buff *skb)
nhoff + offsetof(struct ipv6hdr, daddr));
nhoff += sizeof(struct ipv6hdr);
g->nhoff = nhoff;
skb->cb[0] = nhoff;
parse_ip_proto(skb, g, ip_proto);
return 0;
}
PROG(PARSE_VLAN)(struct __sk_buff *skb)
{
struct globals *g = this_cpu_globals();
__u32 nhoff, proto;
if (!g)
return 0;
nhoff = g->nhoff;
nhoff = skb->cb[0];
proto = load_half(skb, nhoff + offsetof(struct vlan_hdr,
h_vlan_encapsulated_proto));
nhoff += sizeof(struct vlan_hdr);
g->nhoff = nhoff;
skb->cb[0] = nhoff;
parse_eth_proto(skb, proto);
@ -260,17 +255,13 @@ PROG(PARSE_VLAN)(struct __sk_buff *skb)
PROG(PARSE_MPLS)(struct __sk_buff *skb)
{
struct globals *g = this_cpu_globals();
__u32 nhoff, label;
if (!g)
return 0;
nhoff = g->nhoff;
nhoff = skb->cb[0];
label = load_word(skb, nhoff);
nhoff += sizeof(struct mpls_label);
g->nhoff = nhoff;
skb->cb[0] = nhoff;
if (label & MPLS_LS_S_MASK) {
__u8 verlen = load_byte(skb, nhoff);
@ -288,14 +279,10 @@ PROG(PARSE_MPLS)(struct __sk_buff *skb)
SEC("socket/0")
int main_prog(struct __sk_buff *skb)
{
struct globals *g = this_cpu_globals();
__u32 nhoff = ETH_HLEN;
__u32 proto = load_half(skb, 12);
if (!g)
return 0;
g->nhoff = nhoff;
skb->cb[0] = nhoff;
parse_eth_proto(skb, proto);
return 0;
}

84
samples/bpf/test_verifier.c
View File

@ -29,6 +29,7 @@ struct bpf_test {
ACCEPT,
REJECT
} result;
enum bpf_prog_type prog_type;
};
static struct bpf_test tests[] = {
@ -743,6 +744,84 @@ static struct bpf_test tests[] = {
.errstr = "different pointers",
.result = REJECT,
},
{
"check skb->mark is not writeable by sockets",
.insns = {
BPF_STX_MEM(BPF_W, BPF_REG_1, BPF_REG_1,
offsetof(struct __sk_buff, mark)),
BPF_EXIT_INSN(),
},
.errstr = "invalid bpf_context access",
.result = REJECT,
},
{
"check skb->tc_index is not writeable by sockets",
.insns = {
BPF_STX_MEM(BPF_W, BPF_REG_1, BPF_REG_1,
offsetof(struct __sk_buff, tc_index)),
BPF_EXIT_INSN(),
},
.errstr = "invalid bpf_context access",
.result = REJECT,
},
{
"check non-u32 access to cb",
.insns = {
BPF_STX_MEM(BPF_H, BPF_REG_1, BPF_REG_1,
offsetof(struct __sk_buff, cb[0])),
BPF_EXIT_INSN(),
},
.errstr = "invalid bpf_context access",
.result = REJECT,
},
{
"check out of range skb->cb access",
.insns = {
BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1,
offsetof(struct __sk_buff, cb[60])),
BPF_EXIT_INSN(),
},
.errstr = "invalid bpf_context access",
.result = REJECT,
.prog_type = BPF_PROG_TYPE_SCHED_ACT,
},
{
"write skb fields from socket prog",
.insns = {
BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1,
offsetof(struct __sk_buff, cb[4])),
BPF_JMP_IMM(BPF_JGE, BPF_REG_0, 0, 1),
BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1,
offsetof(struct __sk_buff, mark)),
BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1,
offsetof(struct __sk_buff, tc_index)),
BPF_JMP_IMM(BPF_JGE, BPF_REG_0, 0, 1),
BPF_STX_MEM(BPF_W, BPF_REG_1, BPF_REG_1,
offsetof(struct __sk_buff, cb[0])),
BPF_STX_MEM(BPF_W, BPF_REG_1, BPF_REG_1,
offsetof(struct __sk_buff, cb[2])),
BPF_EXIT_INSN(),
},
.result = ACCEPT,
},
{
"write skb fields from tc_cls_act prog",
.insns = {
BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1,
offsetof(struct __sk_buff, cb[0])),
BPF_STX_MEM(BPF_W, BPF_REG_1, BPF_REG_0,
offsetof(struct __sk_buff, mark)),
BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1,
offsetof(struct __sk_buff, tc_index)),
BPF_STX_MEM(BPF_W, BPF_REG_1, BPF_REG_0,
offsetof(struct __sk_buff, tc_index)),
BPF_STX_MEM(BPF_W, BPF_REG_1, BPF_REG_0,
offsetof(struct __sk_buff, cb[3])),
BPF_EXIT_INSN(),
},
.result = ACCEPT,
.prog_type = BPF_PROG_TYPE_SCHED_CLS,
},
};
static int probe_filter_length(struct bpf_insn *fp)
@ -775,6 +854,7 @@ static int test(void)
for (i = 0; i < ARRAY_SIZE(tests); i++) {
struct bpf_insn *prog = tests[i].insns;
int prog_type = tests[i].prog_type;
int prog_len = probe_filter_length(prog);
int *fixup = tests[i].fixup;
int map_fd = -1;
@ -789,8 +869,8 @@ static int test(void)
}
printf("#%d %s ", i, tests[i].descr);
prog_fd = bpf_prog_load(BPF_PROG_TYPE_SOCKET_FILTER, prog,
prog_len * sizeof(struct bpf_insn),
prog_fd = bpf_prog_load(prog_type ?: BPF_PROG_TYPE_SOCKET_FILTER,
prog, prog_len * sizeof(struct bpf_insn),
"GPL", 0);
if (tests[i].result == ACCEPT) {